Field of the Invention
This invention relates to a battery, in particular, a battery having an outer package made of a laminated film.
Description of the Related Art
JP-A-2006-324134 discloses a secondary battery having an outer package having a melt-bonded region formed by melt-bonding portions of a resin layer of a laminated film to each other, and a positive electrode terminal protruded outward from the outer package across the melt-bonded region. This positive electrode terminal has a laminated structure composed of a first region (first layer) made of aluminum, and a second region (second layer) made of Al alloy, copper, nickel or iron, thereby being heighten in mechanical strength.
However, in the secondary battery of the publication, the second region, which is made of Al alloy, copper, nickel or iron, is high in thermal conductivity so that heat is easily conducted from the positive electrode terminal to localized sites of the resin layer of the laminated film, the heat being heat generated when the positive electrode terminal is welded to an external terminal, or Joule heat generated when a large quantity of electric current is caused to flow into the positive electrode terminal. As a result, the resin layer of the laminated film that contacts the positive electrode terminal is partially softened, so as to be declined in bonding strength. Thus, there is caused a problem that the sealing performance of the outer package is declined.